1. Field of the Invention
The present invention relates to an electron-emitting device having a film containing an electron-emitting material, an electron source in which a large number of electron-emitting devices are arranged, and an image display apparatus using the electron source.
2. Related Background Art
Recently, a carbon fiber such as a carbon nanotube (hereinafter referred to as a “CNT”) serving as a cold cathode material is attracting attention. The carbon nanotube is a fullerene having a cylindrical structure in which graphite of several layers or a single layer is wound, and is a new carbon material discovered in 1991 (Nature, 354, (1991) 56). Further, an application of a carbon nanotube to an image display apparatus using an electron source in which a large number of minute electron-emitting devices are two-dimensionally formed is being attempted.
Up to now, there has been known an example of a field emission type electron-emitting device in which a conical cathode electrode is formed on a substrate in a substantially vertical direction, a so-called “Spindt type”. In the Spindt type electron-emitting device, an insulating layer and a gate electrode are formed on the substrate and the conical cathode electrode made of Mo or the like is formed in a hole obtained by micro fabrication. An anode electrode and a phosphor are opposed to the gate electrode.
The above-mentioned Spindt type electron-emitting device utilizes an electron field emission from a sharpened tip portion of a cathode electrode. However, with respect to the device formed by the micro fabrication, it is difficult to increase the number of devices per pixel in the image display apparatus.
In order to reduce a voltage for field emission, it is important to increase an aspect ratio in the sharpened tip portion. However, there is a limitation on sharpening of the tip portion by a micro fabrication technique and it is difficult to reduce an electric field strength required for field emission.
On the other hand, a carbon fiber such as a CNT has a shape of a high aspect ratio with a minute diameter of several tens of nm and a length of several hundreds of nm to several μm. Therefore, when the carbon fiber is used for the electron source, it can be driven at low voltage. In addition, because a large allowable current capacity is obtained, the carbon fiber has a large number of characteristics such as a stable large emission current, which are advantageous on an application to the image display apparatus (for example, see Japanese Patent Application Laid-Open No. 2002-025477).
On the other hand, there has been known an example of an electron-emitting device having a lateral structure (for example, see U.S. Pat. No. 4,728,851 and U.S. Pat. No. 4,904,895). A cathode electrode whose tip is sharpened and a gate electrode to extract electrons from the tip of the cathode electrode are formed parallel to a substrate. An anode electrode is located in a direction perpendicular to a direction along which the gate electrode and the cathode electrode are opposed.
Even in such a lateral type electron-emitting device, as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-052598, 2002-150925, and the like, an attempt to improve a device characteristic is made by using a carbon fiber such as a carbon nanotube for an electron-emitting region.
By using an electron source substrate in which a plurality of electron-emitting devices as described above are formed, an image forming apparatus can be constructed in combination with an image forming member composed of a phosphor and the like.